Abstract: A printer comprises a print head comprising nozzles to selectively deposit liquid drops to selected portions of a receiving surface, a radiation light source to supply first light to the receiving surface, and a drop detector. The drop detector detects a flying liquid drop ejected by one of the nozzles and comprises a detector light source to emit a light beam of second light and a light detector to detect the light beam of the second light. The second light is distinguishable by the drop detector from the first light.

Abstract: Movement detection circuitry is provided for a moveable component of an apparatus having an encoder member having a plurality of spaced regions to cause a response by a first detector and a second detector on the moveable component. First and second detection signal detection signals are received respectively from the first detector and second detector by processing circuitry of the movement detection circuitry. At least one of the first detection signal and the second detection signal is sampled when the first detector and second detector move relative to the encoder member. An error due to any impairment to one the spaced regions of the encoder member is based upon a comparison between the samples from the two detectors. A movement characteristic of the moveable component is determined by the processing circuitry from at least one of the first detector samples and the second detector samples.